I just ran into this with my Phonak Audeo PFE 122 earphones with microphone. I can confirm that earphones with in-line microphones that are compatible with the iPhone will not work with the Nokia N9.

Those of you with standard earphones without in-line microphones and with standard TRS tips are probably okay. People who already own a headset with an in-line microphone and a TRRS tip might need to be more careful. (TRRS tips have an extra section; see the pictures at http://en.wikipedia.org/wiki/TRS_connector#Uses.)

Apparently, the iPhone expects headsets to be wired T-left, R-right, R-ground, S-microphone. (See the great illustration at http://geekspeak.org/blog/2008/08/12...e-headset-plug.) On the other hand, the Nokia N9 wants its ground and microphone in the other order — T-left, R-right, R-microphone, S-ground.

Hopefully, this means that those of us who already own headsets designed to be compatible with the iPhone will just need an adapter to switch the R and S wiring to use our headsets with the N9. I've ordered http://www.meelec.com/MEE_TRRS_Adapt...tr-trrs-35.htm, and I'll try to remember to post back whether this was successful after I get it.

Update 2012/5/29: Please see my updated adapter recommendation.